The Universal Serial Bus (USB) is a commonly used technology to connect peripheral devices to a host machine, such as a computer. In addition to data lines used to transfer data, the USB connectors and cables include power connections, e.g., the VBUS voltage supply and GND ground lines/pins, available to be used to power USB devices using power supplied by the host.
The USB specification and the characteristics of USB device and host design may impose requirements and/or other limitations with respect to USB power connections. For example, the USB specification requires that to be certified USB compliant a device must pass a series of tests, one of which is the “inrush” current test. Inrush current is the short transient current that occurs at startup or other transitions, for example when you first plug in a USB powered device or when a component uses a lot of power during a transition other than first plug in (e.g., USB hard disk drive or “HDD” disk wind up to read or write after an idle period).
USB analyzers are used by manufacturers and other developers of USB devices, software (e.g., drivers), firmware, etc. to monitor and analyze communications on the Universal Serial Bus (USB) and to monitor power usage. For example, communications between a target USB devices and a target host to which the device has been connected via a USB port on the target host may be monitored to ensure the device is communicating properly with the target host and vice versa in accordance with applicable USB standards and protocols. Current and voltage on the VBUS line may be monitored to ensure the device passes the inrush current test and meets design or other requirements.
A hardware USB analyzer typically comprises a stand alone or other hardware device having a first set of connectors to enable the analyzer to be connected so as to be able to observe traffic between a target USB device and a target host; hardware and/or firmware to decode signals observed on the USB connection being monitored into USB packets; and hardware, logic, and/or an external connector to enable the analyzer to be connected to an analysis PC and to forward to the analysis PC traffic observed on a monitored bus.